The present invention relates to a measurement instrument for measuring pollutants in a liquid, such as oil in water, comprising a main unit disposed in a first housing or casing, the main unit having a connection for electricity, and a sensor unit disposed in a second housing or casing, the second housing or casing having connections to a conduit system for that liquid which is to be measured, and sensor means for emitting a measurement signal.
In the pumping of bilge water from vessels, there are stringent restrictions relating to the maximum amount of pollutants, principally oil, which the bilge water may contain if it is to be permitted to pump the water overboard. The present invention relates, in an aspect thereof, to a measurement instrument which is intended for the continuous monitoring of the concentration of pollutants in such water and triggers an alarm or discontinues the pumping if the concentration becomes too high.
Apparatuses and instruments for the above-outlined purpose and of the type intimated by way of introduction are previously known in the art. In such measurement instruments, use has been made of an electric cable communication between the main unit and the sensor unit. This cable communication has, on the one hand, fed the sensor unit with the necessary electricity for its operation, but also fed back measurement signals from the sensor unit to the main unit where signal processing takes place and where measurement values are presented on a display.
If the sensor unit is to be dismounted, for example for calibration, cleaning or general service, it is naturally necessary that the cable communication between the sensor unit and the main unit be disconnected. Since the measurement instrument according to an aspect of the present invention is used in an extremely dirty marine environment, there is a major risk that water may penetrate in to both the main unit and the sensor unit when the cable communication is opened. In addition, there is also naturally a considerable risk of dirtying the contact surfaces in question. Since the currents that are transferred via the cable communication are slight, even a very insignificant level of dirt on the contact surfaces may cause major problems. As a result, it has not previously been possible to carry out replacement or calibration of the sensor unit without access to well-trained service personnel.
The fact that there is an electric communication between the main unit and the sensor unit entails that the electronics in the sensor unit will have an electric potential that is determined by the electric potential in the main unit and that does not necessarily correspond with the potential in the housing of the sensor unit or in the liquid passing through the sensor unit. This may give rise to galvanic currents with attendant corrosion problems.
It is desirable to design the measurement instrument intimated by way of introduction so that the drawbacks inherent in prior art technology are obviated. Thus, it is desirable to design the measurement instrument so that calibration, dismounting, cleaning and other maintenance are substantially facilitated. Further, it is desirable to design the measurement instrument so that problems involving dirtying, leakage and corrosion are eliminated.
According to an aspect of the present invention the measurement instrument intimated by way of introduction can be characterised in that both the first and the second housing or casing have mutually cooperating devices for inductive or capacitative energy transfer therebetween, and that the second housing or casing is secured on the first, or vice versa.